Atomistic investigation into the formation of axial weak twins during the compression of single-crystal Mg nanopillars

Molecular dynamics simulations are performed to provide a detailed atomic-level understanding of the deformation and twinning behavior of single-crystal Mg nanopillars under [ 0001 ] and [ 01 1 ¯ 0 ] compressions. To that end, a new interatomic potential based on the second nearest-neighbor modified embedded-atom method is developed to improve the reproducibility of overall physical properties, particularly in relation to plastic deformation. Further nanopillar compression analysis reveals that the simulation based on the developed potential satisfactorily reproduces the experimentally observed slip and twinning phenomena, consistent with theoretical interpretations. The present simulation results provide visual evidence for differentiated deformation characteristics of single-crystal Mg in different loading orientations and for the detailed nucleation and growth mechanisms of the recently discovered unconventional twins known as “axial weak twins” that exhibit 90° and 62° orientation relationships with the parent matrix. Our investigation reveals that the formation of both weak twins is commonly associated with atomic shuffling in the high-stress state, and the nucleation of the 62° weak twin is facilitated by pyramidal I dislocations.